Tough leader's sarcasm about left wingers in Auckland (4,4)
I believe the answer is:
iron lady
'tough leader's' is the definition.
(Margaret Thatcher was nicknamed the Iron Lady)
'sarcasm about left wingers in auckland' is the wordplay.
'sarcasm' becomes 'irony' (synonyms).
'about' is an insertion indicator.
'left' becomes 'l' (common abbreviation).
'wingers in' means to remove the middle letters (only letters on the 'wings' of the word).
'auckland' with its middle taken out is 'ad'.
'l'+'ad'='lad'
'irony' enclosing 'lad' is 'IRON LADY'.
(Other definitions for iron lady that I've seen before include "at No 10, once?" , "The one who was "not for turning"" .)